The search began at 8 p.m. GMT on Friday, less than an hour after the warrant was issued, and lasted about seven hours.

Following the search the ICO said it was assessing the evidence it had gathered before deciding on its next steps.

“This is just one part of a larger investigation into the use of personal data for political purposes and we will now need time to collect and consider the evidence,” the ICO said on Twitter.

Data probe

The search follows allegations by a whistleblower that the London firm used improperly obtained data on 50 million Facebook users to influence the 2016 US presidential election. Both firms deny wrongdoing.

The ICO is also investigating Cambridge Analytica’s involvement in campaigning around the referendum on Britain’s exit from the EU.

Both incidents highlight the increasing importance of the detailed personal data organisations hold on individuals and questions around how that data is used.

Reports said 18 enforcement officers entered the firm’s premises and left several hours later, as a van thought to be holding gathered evidence drove away from the rear of the building.

The ICO said it is considering whether the data in question was acquired in an unauthorised way, whether there was sufficient consent to share it, what was done to safeguard it and whether Facebook did enough to ensure the data was deleted after the incident came to light.

Growing scandal

Cambridge Analytica said it has been working with the ICO since February to negotiate enforcement officers’ access to the firm’s premises and would continue to help the investigation.

He said checks in 2015 indicated the Facebook data in question had been deleted, but that the company is undertaking an independent audit to verify none of the data remains.

The firm’s chief executive, Alexander Nix, was suspended last week following a Channel 4 broadcast in which Nix appeared to be suggesting ways the company could discredit politicians.

As users have deleted their Facebook accounts in the wake of the scandal, some said they were surprised at the amount of data the company held on them, including metadata on telephone calls and text messages dating back years.